This invention relates to cutting of contour bevels, and more particularly to the cutting of such bevels on workpieces such as flat metal plates.
Heretofore, in the manufacture of gate valves and the like, the plates from which the valves have been cut have often been fabricated from stainless steel. In contour cutting the valve with the older conventional torches and/or mechanical cutters, a substantial length of cutting time such as 1-2 hours was required. Changes in the contour during cutting could easily be handled because the torch head or other cutter moved slowly relative to the work. In recent times the development of plasma torches, which are electrical in nature, has substantially shortened the cutting time to as little as 1-2 minutes for a similar item, with a major speed increase in torch movement.
With very fast cutting speeds, control of the torch position relative to the flat workpiece during contour bevel cutting has become extremely important. It has already been proposed to mount the plasma torch for movement on an arcuate sector having its center of radius lying in the horizontal plane of the flat workpiece. The torch axis would therefor always pass through the said center of radius, no matter what adjusted angle the torch assumed on the sector during contour bevel cutting. In other words, the torch was always precisely aimed at the surface of the flat workpiece.
In the formation of certain shapes from flat plates, such as the above-mentioned gate valves, it is necessary to provide a vertical edge which merges by a very sharp shoulder into a contoured bevel edge and back again. Heretofore, the control of movement of a plasma torch mounted on a sector during cutting has been so slow that sharp changes in the bevel contour, such as shoulders, have not been possible with this system. Thus, the advantages of the sector concept with plasma torch cutting could not be utilized in the manufacture of these shapes.
The present invention is directed to a concept whereby a sector mounted torch may be controlled in such a manner that substantially instantaneous repositioning of the torch and its resultant angle relative to the workpiece are possible.
More specifically, the torch of a machine for progressive contour bevel cutting of flat plates is mounted for controlled positioning and movement on an arcuate sector, the radius of which has a center lying in the horizontal plane of the plate. The torch is mounted for movement between adjustable stops which delineate two torch angles for cutting. A device is provided for substantially instantaneously moving the torch along the sector from adjacent one stop to the other stop. In the embodiment disclosed herein, the said device comprises a fluid-operated piston connected to the torch.